(i) Field of the Invention
The present invention relates to the method of controlling a tension levelling equipment or tension leveller for the correction of a deformation left in the rolled-down strip product such as a cold rolled steel strip, etc. (hereinafter referred to as "the strip product").
(ii) Description of the Prior Art
It is generally known that the rolled-down strip product suffers from such defects of distortion as a partial elongation and a partial bowing and warping, etc. caused from an evenness in the distribution of temperatures in the strip manufacturing process, a lack or reduction of accuracy of, and/or a lost proper adjustment in machines in the strip mill. It is naturally inevitable that such defects of distortion would not only spoil the appearance of the sheet products, thus degrading the commercial value of the product, but also hamper the efficiency of feed throughout the roll-down operation on the strip product, and thus eventually presenting an obstacle to the automation operation of the entire strip production line. Also, this defect would then cause further distortions in the subsequent secondary working procedures. In this connection, there has been proposed a method of controlling a tension leveler in the attempt for the correction of such defects of distortion in the production of the strip product.
Referring first to FIG. 1, there is shown the general layout of a series of rolls and drive mechanisms, such as those incorporated in the typical tension leveling equipment of conventional construction. As shown in this drawing figure, input bridle unit 3 and output bridle unit 4 are provided on the input and output sides of a levelling mill 2, respectively, through which bridle units 3 and 4 an extension of strip 1 is fed under tension in the direction shown by arrows. By aid of a plurality of working rolls 5, 6, 7 which are arranged extending in a zigzag fashion above and below the extension of the strip 1 along the longitudinal direction of the entire levelling mill 2 of non-driven type, the strip 1 is subjected in sequence to the repeated procedures of bending throughout the whole extension of the levelling mill 2. With this sequence of procedures, the strip 1 is given a permanent elongation which is required for smoothing out its distortions, thus obtaining a due correction of distortions involved in the strip 1, accordingly. It is also seen that there is provided between the input and output bridle units 3 and 4 a drive mechanism which is operable with a difference in feeding velocities set to provide a predetermined extent of elongation required on the strip 1.
A required rate of elongation on the extension of strip 1 is obtained by providing a design that gives a difference in velocities of rotation of the input and output bridle units 3 and 4 which corresponds to a predetermined extent of elongation. More specifically, it is arranged that the input and output bridle units 3 and 4 are both connected mechanically to a single main motor 8, while a required difference in rotation velocities, that is a predetermined rate of elongation of the strip product is given by way of a stretching motor 9. In connection with this typical construction, it is known that a group of rolls in either of the bride units 3 and 4, for instance, the group of rolls 4a, 4b, 4c, 4d of the output side bridle 4 is taken for a reference of rotating velocity, while the group of rolls 3a, 3b, 3c, 3d of the input side bridle unit 3 is for a lower velocity of rotation which is equal to a predetermined rate of elongation of the strip product 1. According to this illustrated construction, it is seen that the reference bridle unit 4 is driven directly by the main motor 8 through a set of bevel gears 10b and pinion stand 11b. On the other hand, the opposite side bridle unit 3 is operatively connected to a solar-revolutionary shaft 14 of a planetary gear 13 of a planetary gear unit 12 through a pinion stand 11a and a set of bevel gears 10a. It is also seen that a ring gear 15 is arranged to be driven by the main motor 8 through a pinion 16, while a solar gear 17 is driven by a stretching motor 9 which is, for instance, a direct current motor, respectively. This stretching motor 9 is equipped with a revolution speed control by a direct digital computer system, not shown. With this construction, a required difference in the peripheral velocities (that is, a predetermined rate of elongation) in the reference bridle unit 4 and the corresponding bridle unit 3 may precisely be controlled by way of the stretching motor 9. On the other hand, each roll in the group of rolls belonging to the both bridle units 3 and 4 is connected mechanically with each other so that it has the same number of revolution, respectively. However, on the part of the strip product 1, there occurs a slipping between these groups of rolls from an elongation as produced under the effect of tension rendered thereupon while passing these rolls, which slipping would possibly generate such damages as flaws or like scratches on the surface of the strip product 1. In an attempt to prevent such damage from occurring, there is provided in each of the bridle units 3, 4 a series of slipping clutches of, for instance, a powder clutch type or the like, P1, P2, P3, P4, P5, P6 between the groups of rolls 3a, 3b, 3c and 4a, 4b, 4c and the pinion stands 11a, 11b, as schematically shown in FIG. 1, so as to provide an appropriate cushioning or absorbing effect to such problem of slippings. In addition, there is provided a suitable tension meter TM3 in an appropriate position in line of the strip mill, for instance, between the output side of the levelling mill 2 and the output bridle unit 4 for measuring a tension T6 of the strip product 1. Then, the thus-obtained result of measurement is converted to a measurement signal t3 corresponding thereto, and then is delivered to an arithmetic unit 18 so as to be processed to output signals tp1 through tp6, by which output signals the torque of each of slipping clutches is controlled accordingly so that a slipping between the strip product 1 and each of the groups of rolls may eventually be nullified.
According to this particular arrangement, it is noted that there is provided such a physical relationship between a torque of each clutch and a tension on the strip product 1 passing therethrough as shown in the following equations (1) through (3), and (6) through (8). EQU T.sub.qp1 =(T.sub.2 -T.sub.1).multidot.D/2.multidot.K (1) EQU T.sub.qp2 =(T.sub.3 -T.sub.b 2).multidot.D/2.multidot.K (2) EQU T.sub.qp3 =(T.sub.4 -T.sub.3).multidot.D/2.multidot.K (3) EQU T.sub.q1 =(T.sub.5 -T.sub.4).multidot.D/2.multidot.K (4) EQU T.sub.q2 =(T.sub.6 -T.sub.7).multidot.D/2.multidot.K (5) EQU T.sub.qp4 =(T.sub.7 -T.sub.8).multidot.D/2.multidot.K (6) EQU T.sub.qp5 =(T.sub.8 -T.sub.9).multidot.D/2.multidot.K (7) EQU T.sub.qp6 =(T.sub.9 -T.sub.10).multidot.D/2.multidot.K (8)
where, T.sub.1 .about.T.sub.10 represents a value of tension on the strip product; TM3 represents a tension meter; T.sub.qp1 .about.T.sub.qp6 represents a value of torque of a powder clutch; T.sub.q1 and T.sub.q2 represent torques of the reference bridle rolls 3d and 4a of the input and output bridle units; D represents a diameter of each roll; and K represents a ratio of reduction gears.
In recent years, however, the requirements for an improvement in the quality of the strip product have been growing more and more strict, so that a process of preventing flaws and scratches in the strip product by way of the mere provision of slipping clutches as provided between the strip product and the roll mechanism cannot meet such increasing requirements any longer.
Referring more specifically, according to the typical conventional method of preventing such defects of the strip product 1 as noted above, it is noted as reviewed fully hereinbefore that the torque of each of slipping clutches is controlled following the measurement signal t3 as given from the tension meter TM3, by the assumption that the current tension on a strip before and after the levelling mill 2 is T.sub.5 =T.sub.6. However, it is to be noted that the current value of input tension T.sub.1 at the input bridle 3 and the current value of output tension T.sub.10 at the output bridle unit 4 are out of the range of control on the part of the tension levelling equipment, and also that the current value of tension will be T.sub.6 =T.sub.5 +.alpha. because of a bend loss (including a friction loss) in the strip product 1 when passing through the entire levelling mill 2, which would immediately mean T.sub.5 .noteq.T.sub.6. As a consequence, it is not feasible in practice, as obvious from the equations (1) through (8) above, to attain any positive torque control taken fully in accordance of the actual fluctuations in tensions of the strip product 1, at all.
In consideration of such drawbacks particular to the conventional process for prevention of slipping in the levelling mill as noted above, it would be desirable to attain an efficient resolution for overcoming such inevitable problems particular to the conventional construction.
The present invention is essentially directed to the provision of a due and proper resolution to such inconveniences and difficulties in practice as outlined above and experienced in the conventional levelling mill of the strip product which have been left unattended with any proper countermeasures therefor.